There's a known bug in pre 4.0 versions of Prime with regards to the determinant of matrix, especially if it has complex valued elements.
It was fixed just before the release of Prime 4, one of the reasons that release took so long, and just a couple of more days in the end.
See here:Using Prime 3.0, the determinant function does not handle a matrix with complex numbers. Don't how to fix it.
There still is a bug in Prime (4.0) regarding norm of a matrix.
Luc